Below grade fills are currently in use at many service stations. These fills are located below the surface of the pavement and have spill protection. Typically there exists an annular space between the spill containment and the manhole access. This annular space is a conduit to the soil beneath the pavement for spills that either overflow the spill containment or that fall outside of the containment due to the connecting or disconnecting of the fuel transfer hose or any other spills that occur on the concrete. See FIG. 1 for an illustration of such a below grade fill.
A secondary containment system is a system that collects and contains fluids that leak out of another and primary containment system. For example, a primary containment system may store, pump and deliver hydrocarbon fuels, such as gasoline and diesel oil, at a fueling station. A secondary containment system collects and contains that same fuel if a primary tank, pump or delivery pipe should rupture or otherwise spill the gasoline. A secondary containment system also catches fuel that spills when a fill tube runs over while a fuel storage tank is being filled, for example. While the invention is described hereinafter in connection with a hydrocarbon fuel filling station storage and delivery system, it should be understood that the invention may also be used to protect any other suitable primary containment system.
With the advent of more stringent environmental regulation, it is important to attempt to contain any fuel spillage and prevent passage of such spillage to the ground, where absorption can require removal an treatment of the contaminated ground material. Hence, it is highly desirable to provide a secondary containment system for spillage from a below grade fill.